The ventilatory controlling factors associated with oral augmentation of nasal breathing were investigated in 25 (14 women, 11 men) healthy adults during an incrementally graded bicycle exercise test. Ventilatory variables were measured by separate oral and nasal pneumotachometers integrated with a valveless oral-nasal face mask and a flexible oral catheter. Inspired and expired breath length, nasal flows, nasal ventilation, transnasal pressures, nasal work of breathing, nasal powers, and nasal resistances were measured simultaneously on a breath-by-breath basis and averaged over the 30-s interval before oral augmentation. Subjects participated in a minimum of two separate tests, with statistical analysis focusing on the correlation obtained for nasal work of breathing (r = 0.870), nasal average power (r = 0.838), and average transnasal pressure (r = 0.819) during inspiration and for average nasal power (r = 0.801) during expiration indicates that these variables were the most reliable predictors of the oral augmentation of nasal breathing.